The present invention relates to a method for estimating the temperature of the exhaust gases upstream from a pre-catalyser disposed along an exhaust pipe of an internal-combustion engine.
Systems for controlling the composition of the exhaust gases of intern-combustion engines are known, which require acquisition and processing of a certain series of signals, which can either be measured directly by means or suitable sensors, or can be estimated from other values correlated to the signals, by means of use of predictive models.
For the sake of greater clarity, reference is made of FIG. 1, which illustrates a simplified block diagram of a known system for controlling the composition of the exhaust gases of an engine 20, provided with a pre-catalyser 2, which is disposed along an exhaust pipe 7, in a position which is very close to the engine 20 itself, and a main catalyser 3, which is disposed along the exhaust pipe, downstream from the pre-catalyser 2, in a position further away rom the engine 20.
The control system, which is indicated as 1 as a whole, comprises an oxygen sensor 5, which is disposed upstream from the pre-catalyser 2, and normally consists of a linear LAMBDA or UEGO sensor, and supplies a signal VOX which indicates the quantity of oxygen present in the exhaust gases at the intake of the pre-catalyser 2; a temperature sensor 6, which is disposed downstream from the pre-catalyser 2, between the latter and the main catalyser 3, and supplies a signal VT which indicates the temperature TV of the exhaust gases at the output of the pre-catalyser 2 itself, indicated hereafter in the description by the term xe2x80x9ctemperature downsreamxe2x80x9d; and a control unit 4 which is connected to the oxygen sensor 5 and to the temperature sensor 6, receives the signals VOX and VT, and, on the basis of these signals, serves the purpose of controlling the composition of the exhaust gases produced by the engine 20.
In order to implement satisfactory control of the composition of the exhaust gases, in addition to the signals VOX and TV, the control unit 4 also needs to have available additional values, which, if they are not in specific operating conditions, cannot be measured either directly or indirectly, and which must therefore be estimated on the basis of the operating conditions of the engine 20 (load, number of revolutions etc.), by means of use of predictive models.
In particular, it is necessary to use predictive models in order to estimate the temperature of the exhaust gases at the intake of the pre-catalyser 2, since this temperature cannot be related directly to the signal supplied by the temperature 6 disposed downstream from the pre-catalyser 2, except in specific operating conditions. In fact, the pre-catalyser 2 is normally the source of exothermal chemical reactions, and consequently the temperature of the exhaust gases increases during passage of the latter through the pre-catalyser 2.
Only in cases when the engine 20 is functioning with an air/fuel (A/F) mixture which is significantly greater than the stoichiometric value (equivalent to 14.56) do the exothermal reactions stop, such that the ratio between the temperature of the exhaust gases at the intake and output of the pre-catalyser becomes known.
The predictive models which are used at present to estimate the temperature of the exhaust gases at the intake of the pre-catalyser 2 nevertheless have some disadvantages.
Firstly, the accuracy of the estimates which can be obtained by means of these predictive models is not always sufficient. In particular, during transient conditions between different operating conditions of the engines, the estimates which are supplied by the known predictive models cannot follow reliably and quickly the variations of the temperature values of the exhaust gases.
In addition, the predictive models which are used at present do not take into account differences from the nominal conditions, owing mainly to ageing of the components, and thus, the estimates which these models provide gradually become increasingly less reliable.
The object of the present invention is to provide a method for estimating the temperature of the exhaust gases, which is free from the disadvantages described, and which in transient can provide reliable estimates even in transient conditions, without requiring the addition of further sensors.
According to the present invention, a method is thus provided for estimating the temperature of the exhaust gases upstream from a pre-catalyser disposed along an exhaust pipe of an internal-combustion engine, which is provided with a system for controlling the composition of the exhaust gases, comprising oxygen sensor means which are disposed along the said exhaust pipe, upstream from the said pre-catalyser, and means for piloting the said heater means; the said method being characterised in that it comprises the steps of:
a) determining a first operative quantity, which is correlated to the exchange of heat between the said oxygen sensor means and the exhaust gases; and
b) determining a temperature of the exhaust gases upstream from the said pre-catalyser, according to the said first operative quantity.